A-DAD-A Nonfullerene Acceptor Obtained by Fine-Tuning Side Chains on Pyrroles Enables PBDB-T-Based Organic Solar Cells with over 14% Efficiency

The recent emergence of small acceptor molecules that are nonfullerene (NFSMAs) of A-DAD-A type, particularly Y6, has accounted for the effective organic solar cells (OSCs). A new acceptor derivative denoted as Y18-DMO using 3,7-dimethyloctyl instead of 2-ethylhexyl on pyrroles of Y18 is reported. Y18-DMO shows the optical gap of 1.37 eV, with the highest occupied and lowest unoccupied molecular orbital energy levels at -5.86 and -3.90 eV, respectively. PBDB-T:Y18-DMO-based photovoltaic devices treated for 40 s by solvent vapor annealing in tetrahydrofuran (THF) yield a power conversion efficiency that reaches 14.18%, which is around the maximum efficiencies among the PBDB-T-based OSCs so far. Besides, these devices exhibit an energy loss as low as 0.55 eV while achieving a large open-circuit voltage of 0.81 V.